Xerographic donor development apparatus



April 1968 L. N. NOST 3,375,806

XEROGRAPHIC DONOR DEVELOPMENT APPARATUS Filed May 6, 1965 2 Sheets-Sheet1 95 I O I07 :02 T M 74 FIG 2 INVENTOR.

M M 97 ou|s N. NOST A 7' TORNE Y5 April 2, 1968 L. N. NOST 3,375,805

XEROGRAPHIC DONOR DEVELOPMENT APPARATUS Filed May 6, 1965 2 Sheets-Sheetz I Q Q INVENTOR. LOUIS N. NOST United States Patent 3,375,806XEROGRAPHIC DONOR DEVELOPMENT APPARATUS Louis N. Nost, Rochester, -N.Y.,assignor to Xerox Corporation, Rochester, N.Y., a corporation of NewYork Filed May 6, 1965, Ser. No. 453,640 14 Claims. (Cl. 118637)ABSTRACT OF THE DISCLOSURE Apparatus for developing latent electrostaticimages on a moving xerographic plate in which electroscopic powdermarking particles are uniformly loaded onto donor means and transportedby the donor means into contact with the moving xerographic plate at aplurality of different locations positioned serially along the peripheryof the xerographic plate.

This invention relate-s to xerography and, in particular, to novelapparatus for developing electrostatic images of copy.

In the process of xerography, for example, as disclosed in CarlsonPatent 2,297,691, issued Oct. 6, 1942, a xerographic plate comprising alayer of photoconductive insulating material on a conductive backing isgiven a uniform electric charge over its surface and is then exposed tothe subject matter to be reproduced, usually by conventional projectiontechniques. This exposure discharges the plate areas in accordance withthe radiation intensity that reaches it and thereby creates a latentelectrostatic image on or in the photoconductive layer. Development ofthe latent image is effected with an electrostatically charged, finelydivided material, such as an electroscopic powder, that is brought intosurface contact with the photoconductive layer and is held thereonelectrostatically in a selective pattern corresponding to the latentelectrostatic image. Thereafter, the developed image may be fixed by anysuitable means to the surface on which it has been developed or may betransferred to a secondary support surface to which it may be fixed orutilized 'by means known in the art.

Whatever method is employed for forming electrostatic images, they areusually made visible by developing. Various developing systems are wellknown in the art and include cascade, brush development, magnetic brush,powder cloud, and liquid development, to name a few. Still anotherdeveloping method is disclosed in Mayo Patent 2,895,847 in which asupport member such as a web, sheet or other member termed a donor isemployed to present a releasable layer of electroscopi-c markingparticles to the plate for deposit thereon in conformity with theelectrostatic image.

These various development systems, including the donor method of Mayo,while each offering specific advantages for particular developingsituations, also have their limitations. For example, the generallyadvantageous method of cascade development depends on gravity-flow, thusimposing physical limitations on its position within the apparatus andrequiring elevating means to transport the de veloper from a supply to arelease position. The donor method has been found generally advantageousfor developing electrostatic images offering the advantage of a morecontrolled presentation of developer to the xerographic plate withoutthe physical limitations imposed by the cascade system. Despite theadvantages afforded there- 3,375,806 Patented Apr. 2 1968 Now inaccordance withthe present invention there is provi-dednovel donor typedevelopment apparatus which substantially improves image density andcontrast of developed images as compared to the prior art. With theapparatus hereof, it is possible to develop prints of high image densityand contrast by apparatus designed to present large quantities ofdeveloper to the image bearing surface in a controlled and uniformmanner. Because of its enhanced development properties, this apparatusis rendered suitable for use in automatic copying machines which operateat high rates of speed, and without the attendant handicaps associatedwith prior art devices.

The problems associated with prior art donor development devices andprocesses are therefore overcome in accordance with the apparatus of thepresent invention in which a moving, powder-bearing donor member effectsdevelopment by a series of repetitive contiguous approaches to the imageareas of an advancing xerographic plate. Each approach may compriseactual contact or a close spacing to within about 300 microns betweenthe developer surface and the image areas of the xerographic plate.After each approach and before the next, redistribution means and/ orsupplemental powder loading means respectively redistribute remainingpowder and/or additionally load the donor uniformly. This acts to renewthe depleted donor surface prior to a subsequent approach by increasingthe quantity and the distribution uniformity of the developer powder forpresentation to the latent image.

Accordingly, it is an object of the invention to provide novel apparatusto effect improved development of electrostatic images.

It is a further object of the invention to provide novel apparatus forimproving donor type development in the process of xerography.

It is a still further object of the invention to provide donor typedevelopment apparatus able to produce prints of improved image densityand contrast as compared to prior art donor development apparatus.

It is a still further object of .the invention to provide donor typedevelopment apparatus adapted for high speed, automatic operation. I

For a better understanding of the invention as well as other objects andfurther features thereof, reference is made to the following detaileddescription to be read in connection with the accompanying drawings inwhich:

FIG. 1 is a schematic side elevation of an automatic xerographic copyingmachine employing a first develop ment apparatus embodiment of theinvention; and,

FIGS. 2, 3, and 4 are schematic side elevations of additionalembodiments for effecting development in accordance with the inventionhereof.

For a general understanding of the Xerographic processing system inwhich the invention is incorporated, reference is had to FIG. 1 in whichthe various system components are schematically illustrated as in allXerographic systems based on the concept disclosed in the above-citedCarlson patent, a radiation image of copy to be reprodced is projectedonto the sensitized surface of 'a xerographic plate to form anelectrostatic latent image thereon. Thereafter, the latent image isdeveloped-with an oppositely charge-d developing material to form axerographic powder image corresponding to the latent image on the platesurface. The powder image is then electrostatically transferred to asupport surface to which it may be affixed by a fusing device wherebythe powder image is caused permanently to adhere to the support surface.

In the illustrated xerographic apparatus, original copy to be reproducedis placed on a support tray 10from which it is fed onto a transportapparatus generally designated 11. On the transport apparatus, theoriginal is moved on an endless belt 12, driven by motor 13, to pass theoptical axis of projection lens system 14 that is illuminated byprojection lamp LMP-1. The image of the original is reflected by amirror 15 through an adjustable objective lens 16 and then reflected bymirror 17 downwardly through a variable slit aperture assembly 18 andonto the surface of a Xerographic plate in the form of drum 19.

Xerographic drum 19 includes a cylindrical member mounted in suitablebearings in the frame of the machine and is driven in a clockwisedirection by a motor 24 at a constant rate that is proportional to thetransport rate of the original, whereby the peripheral rate of the drumsurface is identical to the rate of movement of the projected radiationimage. The drum comprises a layer of photoconductive material on aconductive backing that is sensitized prior to exposure by means ofcorona generating device 25, which may be an adaptation of the typedisclosed in Vyverberg Patent No. 2,836,725 that is energized from asuitable high potential source.

Exposure of the drum surface to the radiation image discharges thephotoconductive layer in the area struck by radiation whereby thereremains on the drum a latent electrostatic image in image configurationcorresponding 'to the radiation image projected from the original.

As the drum surface continues its movement, the latent electrostaticimage passes through developing station 26 whereat the latent image isdeveloped by a first embodiment for developing in accordance with theinvention as will be described below.

image is transferred may be of any convenient type, such as paper, andmay be obtained from a supply roll 56,

fed over guide roll 57 and over suitable tensioning rolls being directedinto surface contact with the drum in the immediate vicinity' oftrans-fer corona generating device 53. After transfer, the supportsurface 52 is separated from the drum surface and guided through afusing apparatus 58 wherein the powder image is permanently atfixedthereto. Thereafter, the support surface may be fedover a further systemof guide and tensioning-rolls,

and onto a take-up roll 60 that is driven through suitable drive meansby motor 61.

After separation of the support surface 52 from the drum, a coronagenerating device 64 directs electrostatic charge to the residual powerimage on the drum surface. Thereafter, the xerographic drum surfacepasses through a cleaning station 65 whereat its surface is brushed by acleaning brush assembly 56, rotated by a motor 67, whereby residualdeveloping material remaining on the drum surface is removed. The drumsurface then passes through a second discharge station 68 at which it isilluminated by a fluorescent lamp LMP-3, whereby the drum surface inthisregion is completely flooded with light to .remove any electrostaticcharge that may remain thereon.

Suitable light traps are provided in the system to prevent any lightrays fromreaching the drum surface, other than the projected imageduring the period of drum travel immediately prior to sensitization bycorona generating device until after the drum surface is completelypassed through the developing station 26.

Referring now to the embodiment of the developing apparatus asillustrated in FIG. 1, the apparatus is comprised of an endless powderbearing donor belt 27which is caused to advance by means of motor 33 anddrive roller 31 through a series of sinous bends into and out ofcontiguous approaches to the surface of the rotating Xerographic drum.The belt 27 may be electrically conductive or insulating within rangesto be described and may comprise most any material flexible and durableenough to be formed into an endless belt. The belt may comprise suchmaterials as metal sheets, conductive rubbers, paper, Mylar (a durablefilm of polyethylene terephthalate resin), or the like, governed by suchother factors such as cost, availability, useful life, etc. It was foundthat all types of copy including line copy, continuous tone, half toneand solid area are satisfactorily developed with belt materials havingan electrical resistivity generally not more than 10 ohm centmeters.With electrical resistivity of from about 10 to 1'0 ohmcentimeters, andabove, good quality line copy reproductions are produced whilecontinuous tone and half tone reproductions experience decreased qualityat the higher resistivities.

Before the belt 27 is presented to the drum surface it is initiallyloaded with a thin, uniformly distributed, releasable layer ofelectroscopic marking particles 36, which may be of the generalcomposition and nature as described in Carlson Reissue 25,136. Loadingcan be effected by various techniques known in the art such as wiping,brushing, cascading or the like. In a preferred manner in accordanceherewith, loading is effected by means of a device 35 comprised of acircular brush 38 rotated symmetrically about its vertical axis by motor44 and drive belt 45 while belt 27 passes about supporting rollers 41and 42 and supporting platen 43. The brush is funneled about its centerportion 39 to which marking particles 36 are dispensed from a stationaryfeed hopper 46. The hopper outlet is mounted coaxial with the brush atwhich there is included a gate 47 to supply controlled quantities ofmarking particles to the bristles thereof and which in turn apply theparticles to the surface of the donor belt as it passes below in itsrotating, scufiing action therewith. With the constant relative movementbetween the brush and belt the particles are uniformly distributed ontothe belt surface. Brushes of diameters from about 8 to 12 inches withrotational rates of from about 45 to 68 rpm. distribute the particles atrates of between about 0.2 to 2.0 milligrams per square cm. at beltspeeds up to about 50 inches per second.

After passing from the loading apparatus 35, the belt enters thedeveloping station 26 as it passes about roller 20 to effect a firstcontiguous approach to image areas on the drum surface. Thereafter, thebelt approaches the drum surface repetitively as it passes 'overrotating guide rollers 21, 22 and 23, angularly displaced about the drumcircumference juxtaposed thereto. Intermediate each pair of theaforesaid rollers serving to direct the belt in its sinuous, tortuouspath of drum approaches are off-set guide roller brushes 28, 29 and 30driven by motor 32. The latter guide rollers rotate at a peripheral rateslightly greater or less than the travel rate of the belt as to producea relative surface motion therebetween effective to uniformlyredistribute the remaining developer powder on the belt surface. Thisensures uniform powder'distribution for the next approach to the drumsurface. Optionally, a hopper similar to feed hopper 46 can bepositioned to supply marking particles onto brushes 28, 29, and 30 forreloading the donor belt as the brushes rotatingly brush thereagainst.

Guide rollers 20, 21, 22 and 23 are preferably surface layered with anelastomeric material such as a /5 inch layer of polyurethane flexiblefoam, on a supporting substrate such as aluminum. This aids in providingfor substantially uniform pressures across the width of the donor beltwhere it directly contacts the image areas on the drum. Whenelectrically conductive, the rollers can conveniently be biased to avoltage of opposite polarity as that of the toner marking particles inorder to suppress background charge and prevent its development. Brushes28, 29 and 30 are comprised of a supporting roller surface havingbristles or the like, such as lambs wool or a synthetic material such asnylon (a generic term for a series of polyamide resins made by thepolymerization of a hexamethylene-diamine salt of adipic acid), arnel(cellulose triacetate yarns and fibers), dacron (a synthetic fiber madeby the condensation of dimethyl terephthalate and ethylene glycol), orviscose (fibers of regenerated cellulose).

By the embodiment thus described a donor belt in passing aboutappropriately positioned guide rollers is caused to move into aplurality of sequential contiguous approaches with the drum surface, aspreviously described, in order that each incremental image area thereonreceives marking particles on a corresponding number of occasions. Afterpassing out of each approach, the belt is advanced into brushing contactwith the intermediate brushes which effect uniform redistribution of thepowder particles on the belt surface. This re forms a uniform releasablelayer of particles to renew the depleted surface and provide an optimumcondition for the next approach. Whereas four approaches are illustratedthe actual number can be made to vary with requirements such as speed,density and the like.

In FIG. 2, there is illustrated a second embodiment of donor developmentapparatus in accordance herewith. As there shown, a plurality ofindividual endless separately loaded donor belts are advanced into andout of contiguous relation with image areas to present particles forselective transfer. Loading of each belt is generally effected by meansof two intermediate belts which receive marking particles from apparatus35. The first of the intermediate belts is a main duster belt 72 similarto belt 27 and which is advanced by drive roller 73, driven by motor 74in the direction shown into brushing contact with brush 38 of loadingapparatus 35 and becomes loaded with marking particles similarly asabove. The belt is then advanced around roller 75 optionally into acontiguous approach to the drum surface.

The second of the intermediate belts is duster belt 77 likewise similarto belt 27 and having a surface of fibrous or bristle material such asthat described on the surface of offset brushes 28, 29 and 30 of FIG. 1.The belt is advanced by drive roller 96, powered by motor 97 aroundroller 95 into a scufiing, brushing, particle transferring contact withmain duster belt 72 to uniformly receive particles from belt 72.

Belt 77, after being uniformly loaded with marking particles from belt72, advances in turn into loading contact with each of the individualendless donor belts 101, I

102, 103 and 104 to effect the uniform distribution of particlesthereon. This distribution is effected in the region where theindividual donor belts pass over their respective support rollers 111,112, 113 and 114. Each donor belt passes endlessly over its respectiveguide and supporting rollers which are selectively spaced to provideproper belt tension. 7

Each of the individual donor belts 101, 102, 103 and 104 is similar tobelt 27. After being loaded from belt 77, the surface of each donor beltpasses continuously into and out of contiguous relation with the drumsurface by guide rollers 106, 107, 108 and 109, respectively, similar tothe guide rollers 20 through 23 illustrated in FIG. 1. As each donorbelt passes about its guide roller contiguous to the drum surface,powder marking particles thereon are selectively transferred from thesurface thereof to image areas on the drum. Portions of each belt,depleted by virtue of image development, are then advanced away from thedrum toward their rear support roller to be reloaded with a uniformdistribution of powder marking particles by means of belt 77. Thisre-forms a uniform releasable layer of particles to renew the depletedsurface and to ready the same surface area for the next approach.

In FIG. 3 there is illustrated still another embodiment in accordancewith the invention wherein a duster belt 116, is advanced by driveroller 117, powered by motor 118, to pass over supporting plate 43 inbrushing contact with brush 38 of a loading apparatus 35. The latterbelt advances around tension and support roller 119 to pass into loadingcontact with the horizontal portions of the individual donor belts122-125 as they pass over their respective guide rollers 126 and 127.Fillets 120, supported in the frame of the copying machine facilitatethe movement of the duster belt 116 as it advances sequentially pasteach of the donor belts, preventing indiscriminate dusting of particlesthroughout the machine.

Each of the belts after loading advance over their respective guiderollers 121 driven by motor 24 in a counterclockwise direction to effectthe contiguous approach of the advancing belt portions similarly asabove. Portions of each belt depleted by virtue of development are thenadvanced away from the drum toward their supporting and tensioningrollers to be uniformly reloaded by belt 116. This as before re-forms auniform releasable layer of particles to renew the depleted surface andto ready the same surface area for the next approach.

In FIG. 4, there is illustrated still another developing apparatusembodiment wherein loading belt 84 is advanced endlessly in acounterclockwise direction by drive roller 85, powered by motor 86, in adirectional path formed by the relative positions of the drive rollerand supporting and tensioning rollers 93 and 94. Loading apparatus 35,similar to that described before, loads marking particles onto a dusterbelt 84, supported by plate 43 in the loading region. After being loadedbelt 84 passes in loading contact with donor members in the form ofrollers 87, 88, 89, and 91. The cluster belt effects particle loadingonto each of the rollers in a uniform endless layer for presentation tothe image bearing drum surface.

The donor rollers, comprised of a surface material of the general natureof endless donor belt 27, are rotated via motor 24 and are supported asto effect the contiguous approach of powder on its surface with thesurface of the drum. Depleted surface areas of each roller are rotatedaway from the drum toward belt 84 to be reloaded with powder markingparticles on the roller surface. This, as before, re-forms a uniformreleasable layer of particles to renew the depleted roller surface andto ready the same surface area for the next approach.

Above are described apparatus embodiments for effecting improved donordevelopment of latent electrostatic images on a moving xerographic plateto result in reproductions of improved image density and contrast ascompared to prior art devices and further adapted for high speedautomatic operation. In the various embodiments, the speed of the donorbelts or rollers relative to the speed of the xerographic drum surfaceis commonly 1:1 to effect a touchdown contiguous relation between imageareas and the donor surface. However, the two speeds may be different toeffect a slipping contiguous relation between image areas and the donorsurface.

By the above description, there is disclosed improved donor developmentapparatus. By means thereof a large quantity of toner marking particlesis presented controllably and uniformly to image areas on a xerographicplate. Print development is effected by a plurality of repetitive,contiguous approaches by a toner loaded donor member to all the imageareas on a moving xerographic plate. By the invention herein, the imagedensity and contrast of donor developed prints is improved over priorart donor development methods and apparatus to compare favorably withthe high quality prints developed by, for example, the cascade method.

While the invention has been described with reference to the details andconstruction herein illustrated, it is not intended to be confined tothe exact mechanism shown. It is intended to cover such modifications ordepartures as may come within the purposes of the invention and thescope of the following claims.

What is claimed is:

1. In a xerographic reproduction apparatus wherein latent electrostaticimages of copy are formed on the surface of a moving xerographic plate,developing apparatus to render the latent images visible, saiddeveloping apparatus comprising in combination,

an endless elongated donor member on which to support a uniformlydistributed quantity of electroscopic marking particles for developingimage patterns on the surface of said plates,

loading means containing a supply of said electroscopic markingparticles for loading uniformly onto the surface of said donor member,

donor support means providing a sinuous arrangement for said donormember and including a first plurality of support members securedcontiguously juxtaposed to the plate surface, and a second plurality ofsupport members each intermediate each pair of said first recitedmembers and spaced away from the plate sufiicient to off-set the donormember therefrom,

particle distribution means located at the off-set of said donor memberon its support for uniformly distributing marking particles on the donorsurface thereat, and

drive means to continuously advance said donor member past said loadingmeans and over said donor support means to present the particles to theimage bearing surface of said moving xerographic plate as it advancesover said first plurality of support members.-

2. Apparatus according to claim 1 wherein said particle distributionmeans forms said second plurality of support members and comprisesrotating brush means in brushing contact with the particle bearingsurface of said donor member.

3. In a xerographic reproduction apparatus wherein latent electrostaticimages of copy are formed on a moving xerographic plate, developingapparatus to render the latent images visible, said developing apparatuscomprising in combination,

a plurality of spaced apart endless elongated donor members on which tosupport a uniformly distributed quantity of electroscopic markingparticles for developing image patterns on the surface of said plate,

loading means containing a supply of said electroscopic markingparticles for loading uniformly onto the surface of each of said donormembers,

donor support means for each of said donor members and including a firstsupport means positioned contiguous to the surface of the xerographicplate and second support means spaced away from the plate surface, and

drive means to continuously advance each of said donor members past saidloading means and about their respective support means to present theparticles thereon .to the plate from the position on said first donorsupport means.

4. The apparatus according to claim 3 in which said loading meansincludes a loading member passing in simultaneous contact with each ofsaid donor members on their supports.

5. Apparatus according to claim 3 in which said marking particle loadingmeans includes,

a supply source of marking particles,

a first moving endless belt,

a means to dispense electroscopic marking particles from said supplysource onto the surface of said first moving belt, and

a second moving endless belt to receive electroscopic marking particlesfrom said first moving belt and load said particles onto said donormembers brushing thereagainst.

6. Apparatus according to claim 5, in which said dispensing meansincludes a conical brush member rotating about an axis extendingperpendicular to the path of said first moving belt and in brushingcontact with the surface thereof.

7. In a xerographic reproducing apparatus of the type wherein latentelectrostatic images of copy are formed on a moving xerographic plate,developing apparatus for rendering the latent images visible, saiddeveloping apparatus comprising in combination,

donor means for transporting uniformly distributed electroscopic powdermarking particles contained thereon into contact with said movingxerographic plate at a plurality of different locations positioned alongthe periphery of said xerographic plate,

loading means including a source of supply for uniformly depositingelectroscopic powder marking particles onto said donor means,

means for dispensing electroscopic powder marking particles from saidsource of supply and for depositing said particles onto said donor meansincluding a conical brush member in communication with said source ofsupply, said conical brush member being adapted for rotation about thevertical axis thereof, and

drive means operatively connected to said donor means for continuouslyadvancing said donor means whereby to bring successive areas therealonginto contact with said loading means and said xerographic plate.

8. Apparatus according to claim 7, said dispensing means furtherincluding transport means intermediate said brush member and said donormeans whereby to transport electroscopic powder marking particles fromsaid dispensing means onto said donor means.

9. In a xerographic reproducing apparatus of the type wherein latentelectrostatic images of copy are formed on a moving xerographic plate,developing apparatus for rendering the latent images visible, saiddeveloping apparatus comprising in combination,

.donor means for transporting uniformly distributed electroscopic powdermarking particles contained thereon into contact with said movingxerographic plate at a plurality of different locations positioned alongthe periphery of said xerographic plate,

said donor means including a first plurality of spaced support memberspositioned adjacent the surface of saidxerographic plate at saidplurality of different locations,

a second plurality of support members spaced from said first recitedsupport members, and

an endless flexible elongated donor member passing over said first andsecond recited support members, in a generally sinuous arrangement, saidelongated member making a series of repetitive contiguous approaches tothe image area and contacting said xerographic plate at said firstrecited support members;

loading means for uniformly depositing electroscopic powder markingparticles onto said donor means, and

drive means operatively connected to said donor means 'for continuouslyadvancing said donor means whereby to bring successive areas therealonginto contact with said loading means and said xerographic plate.

10. Apparatus according to claim 9, said loading means including,

a source of supply of electroscopic powder marking particles, and

a conical brush member in communication with said source of supply andin brushing contact with said I elongated donor member, said conicalbrush member being adapted for rotation about the vertical axis thereof.

11. In a xerographic reproducing apparatus of the type wherein latentelectrostatic images of copy are formed on a moving xerographic plate,developing apparatus for rendering the latent images visible, saiddeveloping apparatus comprising in combination,

donor means including a plurality of donor members for transportinguniformly distributed electroscopic powder marking particles containedthereon into contact with said moving xerographic plate at a pluralityof diflerent locations positioned along the periphery of saidxerographic plate;

electroscopic powder marking particles for developing image patterns onthe surface of said plate, donor support means for supporting each ofsaid donor members at a plurality of different locations positionedalong the periphery of said xerographic plate, loading means fordepositing a thin uniform layer of loading means for uniformlydepositing electroscopic powder marking particles onto said donor means,

said loading means including at least one elongated endless flexiblebelt member,

a source of supply of electroscopic powder marking particles, and

a conical brush member in communication with said source of supply andin brushing contact with said elongated flexible belt member, saidconical brush member being adapted for rotation about the vertical axisthereof, and

drive means operatively connected to said donor means for continuouslyadvancing said donor means Whereby to bring successive areas therealonginto contact with said loading means and said Xerographic plate.

12. Apparatus according to claim 11, said donor members comprisingelongated endless flexible belt members.

13. Apparatus according to claim 11, said donor members comprising aplurality of cylindrical members adapted for rotation in contact withsaid xerographic plate.

14. In a xerogr-aphic reproducing apparatus of the type wherein latentelectrostatic images of copy are formed on a moving xerog-raphic plate,developing apparatus for rendering the latent images visible, saiddeveloping apparatus comprising in combination,

a plurality of spaced apart endless donor members on which to support auniformly distributed quantity of electroscopic powder marking particlesonto said donor members,

said loading means including a loading member positioned to pass each ofsaid donor members at a position spaced from the surface of saidxerographic plate,

said loading means further including a source of supply of electroscopicpowder marking particles in communication with said loading member, and

drive means for continuously advancing said donor members and saidloading member.

References Cited UNITED STATES PATENTS 2,579,425 12/1951 George 1181 112,811,465 10/1957 Greig 118637 X 2,851,988 9/1958 Reuter 118-6373,081,737 3/1963 Frantz et al. 118637 3,096,212 7/1963 Rosenleaf 118-1113,251,706 5/1966 Walkup 118-637 X 3,152,012 10/1964 Schaifert 11 8-637FOREIGN PATENTS 889,202 2/ 1962 Great Britain.

CHARLES A. WILLMUTH, Primary Examiner.

P. FELDMAN, Assistant Examiner.

